Adenosine is known to be an endogenous modulator of numerous physiological functions. At the cardiovascular system level, adenosine is a strong vasodilator and a cardiac depressor. In the central nervous system, adenosine induces sedative, anxiolytic and antiepileptic effects. In the respiratory system, adenosine induces bronchoconstriction. In the renal system, it exerts a biphasic action, inducing vasoconstriction at low concentrations and vasodilation at high doses. Adenosine acts as a lipolysis inhibitor on fat cells and as an antiaggregant on platelets.
Adenosine action is mediated by the interaction with different membrane specific receptors which belong to the family of receptors coupled with G proteins. Biochemical and pharmacological studies, together with advances in molecular biology, have allowed the identification of at least four subtypes of adenosine receptors: A1, A2a, A2b and A3. A1 and A3 receptors inhibit, while A2a and A2b receptors stimulate the activity of the enzyme adenylate cyclase. Analogs of adenosine able to interact as antagonists with the A1, A2a, A2b and A3 receptors have also been identified.
Selective antagonists for the A2a receptor are of pharmacological interest because of their reduced probability of potentiating side effects. In the central nervous system, A2a antagonists can have antidepressant properties and stimulate cognitive functions. Moreover, data has shown that A2a receptors are present in high density in the basal ganglia, known to be important in the control of movement. Hence, A2a antagonists can improve motor impairment due to neurodegenerative diseases such as Parkinson's disease, senile dementia as in Alzheimer's disease, and psychoses.
Adenosine A2a receptor antagonists have been disclosed as being useful in the treatment or prevention of Extra Pyramidal Syndrome (EPS), dystonia, restless legs syndrome (RLS) or periodic limb movement in sleep (PLMS) in WO 05/044245, and have been disclosed as being useful in the treatment of attention deficit hyperactivity disorder (ADHD) in WO 02/055083.
EPS is a collective term for a series of adverse neurological reactions associated with the use of antipsychotic drugs. There are six different categories of EPS-related neurological syndromes of which four, dystonia, akathisia, pseudoparkinsonism (parkinsonian syndrome), and tardive dyskinesia, are particularly prevalent in patients taking antipsychotic medication. Dystonia is a painful spasm of the muscle groups of, in particular, the neck, jaw, back, pharynx, and larynx. It is most common in young males being treated with antipsychotic drugs, but can also be associated with the use of cocaine, tricyclic antidepressants, lithium and anticonvulsants such as phenytoin and carbamazepine. Pseudoparkinsonism manifests itself as akinesia (rigidity, stiffness and slow voluntary motion, stooped, shuffling walk) and tremor and these symptoms develop within weeks or months after initiation of therapy. Akathisia manifests itself as strong, subjective inner feelings of distress or discomfort characterized by motor restlessness. Often mistaken for agitation or anxiety, this common syndrome is frequently under-diagnosed and is the least responsive to treatment. Tardive dyskinesia is a late-appearing syndrome associated with chronic use of neuroleptic drugs. It occurs more frequently in older patients and is characterized by stereotypical, repetitive, involuntary, quick choreiform movements of the face, eyelids, mouth, tongue, extremities and trunk.
EPS is more prevalent with the use of typical antipsychotic agents but has also been reported with the use of atypical agents. Typical antipsychotics include loxapine, haloperidol, chlorpromazine, prochlorperazine and thiothixene. Atypical antipsychotics include clozapine, olanzapine, loxapine, quetiapine, ziprasidone, risperidone and aripiprazole.
Akathisia is also a characteristic of RLS and PLMS, as well as PLMD (periodic leg (or limb) movement disorder). RLS is a common disorder that causes patients to have an irresistible and unpleasant desire to move their legs; it usually manifests during periods of inactivity and/or at night, and can disturb sleep. Patients who do not have the typical RLS symptoms, but who do exhibit periodic leg movements that adversely impact sleep, are diagnosed with PLMS. Treatments for RLS and PLMS have included levodopa/carbidopa, levodopa/benserazide, dopamine agonists such as pramipexole and ropinerole, benzodiazepines, opioids, anticonvulsants and iron (ferrous sulfate). RLS and PLMS have been extensively described in the literature, for example by Saletu et al, Neuropsychobiology, 41, 4 (2000), p. 190-9.
Some xanthine-related compounds have been found to be A1 receptor selective antagonists, and xanthine and non-xanthine compounds have been found to have high A2a affinity with varying degrees of A2a vs. A1 selectivity. Triazolo-pyrimidine adenosine A2a receptor antagonists have been disclosed previously, for example in WO 95/01356; U.S. Pat. No. 5,565,460; WO 97/05138; WO 98/52568, U.S. Pat. Nos. 6,630,475, 6,653,315, 6,897,217 and PCT/US05/013454, filed Apr. 19, 2005.